Lag between gears after GTX upgrade

[Boosted Esky]

I've recently swapped out a GT2860RS for a GTX2860R Gen2 and had the engine retuned. There's a tiny bit of lag when changing quickly from 3rd to 4th, 4th to 5th. This never happened with the GT. Could it be that the billet wheel has less inertia and therefore slows down more between gears? The other changes made aside from the turbo is a larger 32mm plumb back BOV relocated to the  throttle body side of intercooler (old BOV was 25mm and on the turbo side) and the pipe between turbo and intercooler stepped up from 2" to 2.5" . I've noticed if the BOV is set too soft the lag was worse. I have set it fairly hard but the lag persists.  Just wanting some advice so I'm not wasting time changing things that don't need to be changed eg: changing the 2.5" IC pipe to 2". I get the feeling this is just a characteristic of the GTX turbo?? Thanks in advance

[Dose Pipe Sutututu]

What car? Also you running an AFM?

[KiwiRS4T]

Increasing the pipe size to 2.5in increases by over 55% the amount of air needed to fill it. Whether this is responsible for your increase in lag I couldn't say....

[WMDC35]

/\ You should usually keep the pipe the same size as the compressor outlet until the intercooler

[The Bogan]

How much pressure does the BOV hold, if your dumping all your pressure you might want to adjust your BOV till it just starts to flutter, a bit.

I believe doing this fixed, a bit, the same issue I had with my STI.

I Basically tightened the thing down till it made the pigeon love call, a bit....

There was no real science behind this, I just wanted the BOV to not dump all the air, how much pressure was retained, f**k knows.

Someone smarter will most likely call me a idiot, won't be the first time.....

[Slap]

I've recently swapped out a GT2860RS for a GTX2860R Gen2 and had the engine retuned. There's a tiny bit of lag when changing quickly from 3rd to 4th, 4th to 5th. This never happened with the GT. Could it be that the billet wheel has less inertia and therefore slows down more between gears? The other changes made aside from the turbo is a larger 32mm plumb back BOV relocated to the  throttle body side of intercooler (old BOV was 25mm and on the turbo side) and the pipe between turbo and intercooler stepped up from 2" to 2.5" . I've noticed if the BOV is set too soft the lag was worse. I have set it fairly hard but the lag persists.  Just wanting some advice so I'm not wasting time changing things that don't need to be changed eg: changing the 2.5" IC pipe to 2". I get the feeling this is just a characteristic of the GTX turbo?? Thanks in advance

They are correct about the amount of air that has to be compressed, even though it flows more it won't have as much response due to the time it takes to spool enough boost.

Also the larger bov will allow quicker and more air to be released meaning even more to fill. That's why adjusting it will help a bit.

 

On the bright side your car should make more power up higher in rpm with 2.5" over 2".

 

 

Also worth a mention is that the plumb back needs to be between the afm and turbo as it has usually accounted for the air blown off.

I angled mine to shoot at the turbo fins to help keep inertia.

If it's to close to the afm or it blows back through it ...isn't great.

[Boosted Esky]

Wow a lot of replies thanks. There's no AFM and plumb back is angled on the intake so that's all good. I actually just had the car at the drags Wed night and have gain 3 tenths of a second with this new set up so I'm pretty happy with where it's at. BOV is set hard so it doesn't dump all the charge and the 2.5" pipe doesn't seem to affect things too badly now that I've had a good chance to test it. I'm sure though that a 2" pipe would improve the symptom.  Cheers

[Boosted Esky]

Only a short run to the intercooler. Intercooler inlet is 2.5"